I think the reason is that there is no development at all. It was basically made into a companion to the Adonit Jot Script. This device became completely obsolete with the release of the Pencil and instead of changing the app and its concept, Evernote decided to freeze the app as it was. At the same time they introduced this half-hearten drawing functionality within Evernote, but never developed this in a real functionality for handwritten notes.
How essential handwritten note taking has become for the iPad is obviously by looking at the Top 20 best selling iOS apps of 2018: GoodNotes 4, Notability, MyScript Nebo, Noteshelf 2, Notes Plus - 5 out of 20 best selling apps in 2018 are specific apps for handwritten notes with the Pencil.

No, it is actually not heavily developed! The last update was in January - no support for iOS 12, no support for the new iPads and of course no support for Pencil 2. It does not even support Pencil 1! Yes, I used Penultimate for years, but that was before Apple made the iPad a "real" note taking device by releasing the iPad Pro and Pencil in 2015. Penultimate and Evernote were never really updated for the iPad Pro and its possibility for taking hand written notes in a never before seen quality. I am pretty sure you don't have an iPad Pro and a Pencil and you never used one, right?

I know there was never a proper update to support the "old" Pencil and handwriting notes in Evernote for iOS is not really supported anyway, but wouldn't the release of the new iPad Pros and the great new Pencil be good reasons to finally make Evernote suitable for note taking on iPads? I mean you could start by just supporting Pencil 2 (double tap) and then step-by-step include full support for handwriting notes. Any plans?

Would be very inconvenient, because a handwritten note in Apple Notes is always one scroll page, that gets longer and longer. The procedure of transferring a 10 screens long note to Evernote would be cumbersome.

Evernote for iOS behaves differently than Evernote for Windows or Evernote for macOS when displaying transparent pictures. It uses a black background instead of a white background. This causes a big problem for the new handwriting functionality of Apple Notes in iOS 11. If you export a handwritten note of Apple Notes via sharing to Evernote, the resulting note in Evernote will be a picture with black text on black background. So it's unreadable.
Could you please make the background white for pictures with transparency in Evernote for iOS like it is in the other versions of Evernote?

Yes, it is not possible to add a normal note. How is it even possible to release such an update? It was obviously not tested, not even once. But even worse: There is no immediate update to fix this fundamental error. I wonder if Evernote is even noticing this as obviously nobody at Evernote is actually using their own Watch app.

Yes, but it is not needed. As I said, the normal PDF that is generated by GoodNotes contains the graphics of the writing AND the text. That's why the text of the handwritten PDF from GoodNotes is searchable in Evernote.

I think this thread is still about a replacement of Penultimate and handwriting with Apple Pencil. So per definition not for Android.
I tried Notability and GoodNotes and I think GoodNotes is currently the best Penultimate replacement. It includes a handwriting indexing and the exported PDFs include the recognized text as well, so they are searchable in Evernote. But of course the actual exporting of each note(book) to Evernote needs many taps. I really hope Penultimate is not completely dead and Evernote will come up with a update with complete Pencil support.